Is it possible to create a website that has similar content to other quite developed websites and then make it better to the point of attracting customers away from the more established websites? What does it take?

For example there are a ton of websites reviewing PCs, Cameras etc. Would it be possible given the current environment to create a website that could cut into the hold that the entrenched websites have now or is it better to try and find a completely original idea?

It would take a lot of money and a lot of time but it is do able. If you do a yahoo site explorer search for back links on the domain you want to bump off it's very likely you will find find hundreds or even thousands of backlinks to that domain (if you are going after something like PCs or Cameras)so you would need to get more backlinks and equally as good on page optimization if you want to out rank them.

Your other alternative would be PPC marketing, but depending on the terms of the company (if you can even use their name in your marketing) and the cost per click (CPC) this could cost you a great deal of money as well. (possibly upwords of $1 a click)

So, yes it is possible to do it the SEO route with enough time and energy spent, but we are talking a couple years here. If you are trying to make money NOW you would be better of to target a smaller niche or maybe even one particular product and try to dominate that way.

if you want to create a website which is the same with other website then make sure that you are not copying the whole design. exact more effort to redesign the website as much as possible then create quality content for your website.

It's usually better to have something unique about your site even though it may cover a similar topic to the popular sites. Think about guest posting on popular sites in your niche in order to attract readers who have an interest in your subject area.